Steam utilization system



Sept. 27, 1955 A. G. ARBOGAST 2,719,007

STEAM UTILIZATION SYSTEM Filed Nov. 7, 1952 1N VEN TOR.

United States Patent STEAM UTILIZATION SYSTEM Alva G. Arbogast, Charleston, W. Va. Application November 7, 1952, Serial No. 319,210

6 Claims. (Cl. 237-9) This invention relates to steam utilization systems, and more particularly to an improved system of the general type disclosed in applicants copending application Serial No. 182,788 entitled Pressure Differential Control System for a Closed Steam Boiler Return System, filed September 1, 1950, now Patent 2,626,756 issued on January 27, 1953.

A main object of the invention is to provide a novel and improved system of control for minimizing the heat loss in a steam utilization system of the closed type, the improved control system involving relatively simple apparatus, providing a substantial improvement in efficiency and economy in the utilization of fuel, and functioning to prevent heat loss in a closed steam utilization system by substantially preventing the generation of flash steam.

A further object of the invention is to provide an improved steam utilization system of the closed type wherein a substantially constant differential pressure relationship is established between the steam lines which supply steam for utilization and the condensate return lines which carry the hot steam condensate away from the machinery or equipment in which the steam is utilized.

A still further object of the invention is to provide an improved system of control in a steam utilization system of the closed type wherein excessive heat loss due to flash steam generation in the condensate return lines is effectively prevented, whereby maximum utilization of the heat generated in the system is provided.

A still further object of the invention is to provide an improved system of control to establish and maintain a substantially constant differential pressure relationship between the steam supply lines and the condensate return lines in a steam utilization system of the closed type, wherein sulhciently accurate control is provided to have the steam utilization equipment and the steam boiler at the same elevation or to allow the boiler to be located above the steam utilizing equipment, the control system of the present invention being arranged so that just enough difference in pressure between the steam supply lines and the condensate lines may be maintained to permit the condensate to flow back into the condensate receiver, from whence it may be pumped back into the boiler, regardless of the relative elevation of the boiler and the utilization equipment.

A still further object of the invention is to provide an improved control means in a steam utilization system of the closed type wherein a substantially constant difference in pressure between the steam supply lines and the condensate return lines may be maintained and may be set at a value just high enough to lift the condensate from the low pressure side of the steam utilization equipment back into the condensate receiver, whereby flash loss may be held at a minimum, thus minimizing waste of steam in the system.

A still further object of the invention is to provide an improved steam utilization system of the type disclosed in applicants U. S. Patent 2,626,756, with restrictions or orifices in place of steam traps, permitting the extraction "ice of steam from each utilization device employing the latent heat of the steam to perform its function, such as for drying wet material, for molding plastics, for heating liquids, or for supplying heat to processes requiring such heat, the improved system incorporating connections to the condensate receiver for carrying steam from said receiver to other steam utilization equipment wherein the latent heat of the steam in the receiver may be employed for heating purposes.

A still further object of the invention is to provide a steam utilization system of the type disclosed in applicants U. S. Patent 2,626,756, wherein means are provided for supplying steam to additional steam utilization equipment from the condensate receiver, auxiliary differential pressure control means being provided to maintain a high differential pressure on the system at times of steam extraction to auxiliary utilization equipment from the condensate receiver without the necessity of disturbing the low differential pressure control setting or adjustment.

Further objects and advantages of the invention will become apparent from the following description and claims, and from the accompanying drawings, wherein:

Figure 1 is a schematic diagram of an improved steam utiiization system constructed in accordance with the present invention.

Figure 2 is an enlarged longitudinal cross sectional view of one of the steam flow restricting elements employed in the steam line between each primary steam utilization device and the condensate receiver of the system illustrated in Figure 1.

Referring to the drawings, and more particularly to Figure 1, 11 designates a steam boiler and 12 designates the steam supply line connected to thehigh pressure side of the boiler 11. Designated at 13 are steam utilization devices which may be machines, heating devices or the like, wherein heat is extracted from steam to perform useful functions. Each utilization device 13 is connected to the steam supply line 12 by a conduit 14. Designated at 15 is the condensate return line, the return conduit 16 of each of the devices 13 being connected to the return line 15 through a restriction element 17 and a check valve 18.

As shown in Figure 2, the restriction element 17 may its associated utilization device 13. The size of the aperture 52 is determined in accordance with the loading imposed by the associated utilization device 13 on the system and also depends upon the desired rate of steam flow from the utilization device to the condensate receiver, shown at 19.

Designated at 21 is the boiler return line which connects the bottom of the condensate receiving tank 19 to the boiler 11 and which includes a pump 22 and a check valve 23. The pump 22 is driven by a motor 24 which is energized from the power lines shown at 26, 26 through a conventional float controlled switch 27 connected to the tank 19 in the manner schematically shown in Figure l. The switch 27 is well known per se and forms no part of the present invention. tank 19 and is arranged so that the motor 24 will become energized responsive to a rise in level of the condensate in the tank 19 to a predetermined height. Therefore, the pump 22 will not become energized until suflicient condensate has collected in the tank 19 to bring the level thereof in the tank to the predetermined height for which Said switch 27 is connected to they provided -with-a F-fitting 29. Connected to one arm of the l7-fitting-u29 .is a conduit-30 .which-includesa first...

solenoid valve 31 which is normally closed. Conduit 30 is connected to the high pressure line 12. Connected to which :includesa"second 'normally closedsolenoid valve 3132 'Conduit-30"is likewise' connected' to the high pressure steam line ll Connected -to the'=top of the condensatetank19 is a conduit 55 communicating with the atmosphere and' includingza normally closed solenoid valve 56,"which, when energized; opens the conduit 55 and allows t-hetank 19 to be vented'to atmosphere.

When the first solenoid valve 31 is energized, the conduit' 30 is openedandallows high pressure steam to be delivered directly to the fcondensate tank 19. Likewise,

when the 'secondsolenoid' valve 31" is energized, the conduit 30 is' opened and -allows'steam* to be delivered from the high'zpressure line 12 to the condensate tank.

As shown in Figure 1'; one-terminal of each of the solenoids of thevalves 31, 31' and 56 are connected by respective conductors 57,58" and 59' to the line wire 26. The remaining terminal of the solenoid valve 31 is connected' by a wire 43 to one terminal 40 of a pressure responsive switch device 35 similar to Minneapolis Honeywell-Difierential Pressuretrol Model P606A described in detail in -applicants above mentioned U. S. Patent 2,626,756:

Lin'ewire 26Tis connected by a conductor 44 to the intermediate=terminal39 of switch device 35, and the remaining terminal of the solenoid valve 56 is connected by a wire 42 to the remaining terminal 38 of the switch device 35."

As-shown-in Figure- 1, one side of the pressure responsive switch-device 35 is connected by a conduit 36 to the steam supply line 12 and the other side of said pressure responsive device is connected by a conduit 37 to the condensate tank 19. The switch device 35 may be set so that wheri -the pressure differential between the conduits 36 and-37 is substantially less than a predetermined value, the terrninals 38 and 39 will'be bridged. When thus set, the switch' device will operate to bridge the terminals 39 and 40 when the pressure diflierential between conduits 36 and -exceeds said predetermined value. When the pressure difierential between conduits 36 and 37 is substantially equal to said predetermined set value, the switch device--35 will be in a neutral condition and both terminals 38 and 40 will be disconnected from terminal 39. It will therefore be apparent that when the pressure differential between-the steam-supply-line 12 and the condensate return line 20 is below a predetermined desired value, the

terminals 38 and 39 will be bridged. The respective solenoid valves 31 and 56 are thus controlled by the pressure-responsive switch device 35 so that when the pressure'differential between the conduit 12 and the condensate-tank 19 is below the predetermined set value, the

sure diflerential is substantially equal to the preset value above mentioned, the switch device 35 operates to disconnect the terminal 38 fromterminal 39, thereby deenergizing valve 56 and allowing said valve to close. larly, when the pressure diiferential across conduit 12 and tank19 exceeds the'predetermined set value, the switch device 35 functions to bridge the terminals 39 and 40; energizing the valve 31 and causing said valve 31 to open,

whereby the steam from the supply line 12 is admitted into tank"*19 through the conduit 30 thereby increasing the pressurefrom the. tank 19 and reducing the, pressure differential between the tank and the supply line 12.

when the desired predetermined differential pressure is established between theconduit 12'and tank ,19,"the,"

Sirni-' switch device 35 functions to open the connection be-' tween terminals39 and 40, thereby. deenergizingthevalve.

31 and causing said valve to close. It will therefore be apparent by setting the pressure-responsive switch device 35 to a predetermined setting, the pressure differential between the steam supply line 12 and the condensate tank 19 may be held and maintained at a value just sufficient to lift the condensate through restriction elements 17 back into the condensate tank 19, regardless of the relative elevations of the condensate tank 19 and the devices 13. It is therefore possible to minimize the flash loss in the system, and therefore to minimize waste of heat due to flash loss.

In operation of the system above described, steam from the boiler 11 flows to the steam' heated equipment 13 through the supply line 12 and the conduits 14. As heat is drawn from the devices 13, condensate forms in the devices and is released through the restriction devices 17 into the return line 15,.whence the condensate flows through the condensate return conduit 15 into the condensate tank 19. The condensate accumulates in the. tank 19 until it reaches a predetermined, level, at which time the float operated switch 27 closes and starts-the motor 24 connected .to the pump 22. The pump 22 re-., turns the condensate through the conduit 21 to the boiler. r and continuesin operation ,until the liquid level.in the condensate tank 19 drops to a predetermined low point.

When said low point is reached, the pump 22 is deener: gized; As will be understood by those skilled in the art,

the correct. level in the boiler 11 is maintained by a separate systemhaving no relation to the condensate return system above described, and operating separately fromdifferent control'elements, and having an independ:

ent source of water.

As.is describedin applicants above mentioned patent,

whenwthe boiler 11 is fired and starts to build up pressure in the steam supply line, the steam first enters the equipment 13 and displaces the air within the equipment, and .at the same time condenses rapidly. The air and" condensate fromzthe equipment pass through the orifice devices 17 and out into the main return line 15. The air and cold condensateflow, through said return line into the tank,19, wherethe condensate begins to accu-v mulate-and the air passes out of valve 56 to the atmosphere, said valve being open, since there is no differential pressure between conduits 36 and 37. Valve 56 will remain open as long as less than the predetermined value of differential pressure. exists between conduits 36 and 37.-' The.venting of thecondensate tank 19 continues until :the :boiler steam .pressure:builds up sufliciently so thatdhelimiting ditferentialqpressure between conduits 36 and.37.is reached. At this time, the valve 56 becomes deenergized; and closes. During the time previous to the closing:of the-valve 56, all air hasbeen removed from theequipment .13 and the return lines, and the condensate is entering the tank 19 in a hot-condition. As the boiler continuesto build-up pressure, the pressure in the condensate return system rises along ;.with it, but always remains apredetermined ditference below the boiler supply pressure.

The above paragraph/explains how air is purged from the system when starting from a cold no-pressure condition to establish the desired differential pressure. From thepointwhere said.differential'pressure is established, onexof .two. different conditions may occur:

1. Thecondensate may not come up to full working temperature, under which circumstances the pressure in the-return-line*would-lag behind the rise in boiler pressure. The'differ'entialpressure control switch device 35 would sense this condition, because the differential pressure tends to increase beyond the predetermined diiferential-pressure setting, The increase in differential pressurebeyond the predetermined set valuecauses the switch device 35 to bridgethefterminals, 39and 40, opening valve 31"'and causing steam to be admitted into the condensate tank 19 from conduit 12 through conduit 30. This action would continue until the pressure in the tank 19 has risen sufiiciently to re-establish the predetermined pressure differential between the conduits 36 and 37. When the desired predetermined pressure diflerential has been re-established, the switch device 35 moves to its neutral position, opening the connection across the terminals 39 and 40 and deenergizing the valve 31, causing said valve to close. This places the switch 35 in a neutral position and establishes a balanced condition wherein the steam from the hot condensate is balancing the demand for pressure most of the time after the system is hot.

2. After the system has been started and the desired differential pressure has been reached, if the condensate is up to full saturated temperature, the following operation may occur: The pressure in the condensate return line may rise gradually to a point where the differential pressure is less than the preset value, causing the switch device 35 to operate so as to open the valve 56 and causes steam to be vented from the condensate tank 19 until the desired differential pressure is established. As soon as the desired differential pressure is established, the switch 35 moves into neutral position and remains therein until the system again becomes unbalanced.

It will be therefore apparent that the system thus far described will operate to maintain the return system to the condensate tank 19 at any desired setting below that of the steam supply pressure. The desired differential will remain substantially constant as the steam supply pressure fluctuates over any range greater than the differential pressure setting. The present system above described not only saves fuel by minimizing flash loss, but increases the capacity of the boiler by returning the condensate thereto at a few degrees below the boiler water boiling point, thus relieving the boiler of the necessity of raising the water to this temperature.

If the condensate tank 19 and the return line 15 were not maintained at relatively high pressures, there would be an excessive loss of heat due to steam condensate giving up flash steam as the condensate is released across and through the restriction devices 17 into the condensate return line. The present invention operates to maintain the return system under a constant relative pressure lower than the boiler pressure only by an amount sufficient to produce flow of the condensate back to the condensate tank 19. By keeping the differential pressure as low as possible, namely, just low enough to provide proper condensate drainage, flash loss is kept down to a minimum value, thereby providing maximum fuel economy.

In accordance with the present invention, additional heat utilization equipment may be supplied with steam from the condensate receiver 19, for example, a heat utilizing device 57 may be supplied with steam from the condensate receiver 19 by means of a connecting conduit 58 provided with a manual control valve 59. The utilization device 57 exhausts to the open vent line 55 through a discharge conduit 60 provided with a check valve 61 and a steam trap 62. It will be understood that the vent line 55 may discharge into conventional boiler feed equipment at atmospheric pressure.

It will be further understood that the pressure of the steam in the condensate tank 19 is substantially above atmospheric pressure since it is only a small differential below the pressure in the steam supply line 12. When the valve 59 is opened, a substantial drop in pressure will take place in the condensate receiver 19. The atmospheric vent valve 56 will be closed and the pressure-responsive device 35 will operate to open the steam supply valve 31 in an attempt to supply suflicient steam to bring up the pressure in tank 19 to restore the predetermined differential pressure setting of the switch device 35. However, the valve 31 is dimensioned only just large enough to maintain the low differential control and hence cannot supply suflicient steam to the condensate receiver 19 to keep the pressure within the receiver from falling still further as a result of steam. being withdrawn from the condensate receiver.

During the normal period of operation when the valve 59 was closed, the orifice devices 17 were under low pressure difierences thereacross and were passing only condensate with merely traces of steam. With the valve 59 opened the dilferential pressure increases to a substantially higher value and in so doing increases the discharge rate of the condensate flow beyond the condensing rate of the utilization equipment associated with the orifice device.. Therefore, the condensate is blown freely through the orifice device and steam passes through the orifice along with the condensate for a brief period. Thereafter, re-evaporation takes place rapidly, since the condensate passes from a zone of higher pressure on the inlet side of the orifice to a zone of lower pressure on the receiver side of the orifice, with enough diflerence in saturation temperature in the two zones to cause re-evaporation due to the relatively small actual temperature difference between said two zones.

Designated at 63 is an additional pressure responsive switch device connected across the switch device 35, as by the respective conduits 64 and 65. The contacts 66 and 67 of the switch device 63 are connected in circuit between the line wire 26' and the energizing winding of the valve 31, one terminal of said energizing winding being connected by a conductor 68 to the switch contact 67 and the opposite terminal being connected by the conductor 58' to the line wire 26, as above described. The contacts 66 and 67 are normally open, and are closed responsive to a predetermined pressure difference between the conduits 64 and 65, said pressure difference being substantially greater than the pressure differential required to open the solenoid valve 31.

When the pressure in the condensate tank 19 drops sufficiently, due to the opening of the valve 59, the pressure differential between the steam supply line 12 and the condensate tank reaches the value required to operate the switch 63, closing the contacts 66 and 67, whereby additional steam from the high pressure line 12 is admitted into the condensate tank 19 through the conduit 30 and the open valve 31'.

The pump 22 is a low head pump and will not pump against more than a predetermined difference of pressure between the condensate tank 19 and the boiler 11. Since the additional utilization device 57 might extract enough steam to cause the difference between the boiler pressure and the condensate tank 19 to exceed the maximum head against which the pump 22 can operate, the pressure responsive switch 63 controls the maximum pressure differential by allowing additional steam to be supplied to the condensate tank 19 from the high pressure line 12 over and above the steam supply to said condensate tank through the conduit 30 so as to prevent the pressure differential between the condensate tank 19 and the supply line 12 from increasing to a value beyond which the pump 22 cannot function.

Therefore, the system is so arranged that when the additional steam utilization apparatus 57 is supplied with steam from the condensate tank 19, as by opening the valve 59, the original pressure differential between the steam supply line 12 and the condensate receiver 19 is substantially increased to a new value and the pressure responsive switch device 63 will operate to prevent this new value from being exceeded, the new value being still within the limit required for proper operation or" the pump 22.

When the valve 59 is closed, cutting off the supply of steam to the auxiliary utilization device 57, the pressure rises in the condensate receiver 19, causing the high differential control valve 31' to close. The pressure in the condensate receiver 19 continues to rise as a result of steam being supplied thereto through the orifice de vices 17 and through the valve 31 and the steam supply conduit 30. Eventually, the pressure in the condensate tank 19 rises to a sufiicient value to satisfy the low differential condition, at which time the valve '31 closes and the. system again becomes balanced at the' low differential condition. Under these final conditions, the orifice devices 17. pass condensate in liquid form as fast as the'condensate forms in the utilization devices 13.

Obviously, steam traps employed-in the return lines 16 would not permit steam to -be taken from the utilization devices 13 to supply the auxiliary utilization device 57, if valve59 is opened as abovedescribed. Therefore, it is necessary to employ an orifice or restriction device, such as the device 17, in-or'der to at timesbe able to cause an actual flow of steam through the devices 13. It will be further noted that steam will enter a steam heated machine equipped with a steam trap only at the rate at which the steam is being condensed within the machine as the result of heat being released bythe machine-or device. The steam trap will trap s'teamjust as soon as it appears within the trap, thus preventing steam from flowing through the machine. This means steam enters the steam chamber of a heat exchanger at the exact rate that the steam within the steam chamber is condensing, and-no faster, and cannot be made to flow through the machine because of the steam trap on-the discharge side of the machine. By removing the steam traps and replacing them-with orifices or-restriction devices, such as the devices 17, the rate of flow of steam through the utilization devices 13 may be greatly increased, thus increasing the rate of heat exchange through the structure of the devices, since it is Well known that motion or flow of fluids on opposite sides of a heat exchanger wall increases the rate of heat transfer through the wall materialfar above the rate of heat exchange through the same wall when one or both of the fluids are static or motionless. Therefore, when the devices 13 are heat exchange devices, improved performance is provided by the use of orifice devices, such as devices'17, in the return lines of the utilization devices in place of steam traps. The rate of heat exchange is greater when the utilization device is equipped with orifices instead of steam traps even when the system is on the low ditferential type of operation such as that disclosed in applicants above mentioned patent, and even when no steam is being extracted from the condensate receiver 19.

The orifice devices 17 may be of any suitable type, such as the type illustrated in Figure 2 having fixed apertures, or may be of the adjustable needle valve type.

In a typical mode of operation of the system, the switch 63 closes when the pressure in the condensate receiver 19 drops approximately 30% below the boiler pressure, at

which point steam is bled into the receiver 19from the high pressure line 12 through the conduit 30 to prevent a further increase in the differential pressure.

In a typical installation, the pressure in the condensate receiver 19 may be two or three pounds below the boiler pressure under normal conditions, namely, with the valve 59 closed. When the valve '59 is opened, steam begins to flow from the condensate receiver 19 into the utilization equipment 57 causing an increase in the differential pressure across all the orifices 17 in the system, as Well as between the boiler line 12 and the return system. The original low differential control switch 35 senses this increase beyond its control setting and immediately opens valve 31 in trying to maintain the preset low differential pressure. Valve 31, being a small valve in relation to valve 59, and the load represented by the device 57 being relatively large, cannot supply enough steam to keep the pressure in the condensate receiver 19 from falling still further. As the pressure falls 'in the receiver, the pressure ditferential increases across each orifice device 17 in the system, allowing condensate from each device 13 to blow through the orifice device so rapidly that the orifice device begins to pass steam and condensate, thus causing steam to actually flow through each device 13 into the return receiver 19.

The load on the utilization device 57 may be high enough tokeep the pressure in the condensate tank 19 falling. As soon 'as the'pr'essure in the tank 19 falls to the set point of the high differential control switch 63, this switch will bridge contacts 66 and 67 to energize the valve 31 and allow steam to be bled from the high pressure line 12 directly into the condensate tank 19 through the valve 31. Valve 31 is designed to provide a much greater rate of flow 'therethrough than valve 31. Therefore, as soon as valve 31 opens, the fall of pressure in the tank1'9 is checked. Valve 31 will intermittently open and close, as necessary, to prevent the pressure differential from increasing beyond the maximum desired value. Under these conditions, the orifices 17 are working at a pressure differential beyond the point where they were designed to carry condensate only, and now pass steam and a small amount of condensate to the tank 19. As above explained, as soon as the valve 59 is closed, the load 57 is removed from the system and the pressure differential will be brought back to the low differential point, in which condition the valves 31' -and 31 are closed and the low differential condition is maintained. in the low differential condition, the orifice devices 17 pass only condensate from the utilization devices 13 into the return system.

While a specific embodiment of an improved steam utilization system has been disclosed in the foregoing description, it will be understood that various modifications within the spirit of the invention may occur to those skilled in the art. Therefore, it is intended that no limitations be placed on the invention except as defined by the scope of the appended claims.

What is claimed is:

1. In a steam utilization system, a boiler, a steam utilization device, a condensate collecting chamber, conduit means connecting said boiler, utilization device device and chamber to define a closed system, a vent valve connected to said chamber, additional conduit means connecting the high pressure side of the boiler to said chamber, a second valve in said additional conduit means, a pressure-responsive device connected between said chamber and the high pressure side of the boiler and arranged to selectively control said valves in accordance with variations of the difference in pressure between said chamber and the high pressure side of the boiler and being further arranged to maintain a substantially constant difference in pressure, and a restriction in the first-named conduit means between the utilization device and the condensate collecting chamber.

2. In a steam utilization system, a boiler, a first steam utilization device, a condensate collecting chamber, conduit means connecting said boiler, utilization device and chamber to define a closed system, a vent valve connected to said chamber, additional conduit means connecting the high pressure side of the boiler to said chamber, a second valve in said additional conduit means, a pressure-responsive device connected between said chamber and the high pressure side of the boiler and arranged to selectively control said valves in accordance with variations of the diiference in pressure between said chamber and the high pressure side of the boiler and being further arranged to maintain a substantially constant difference in pressure, a restriction in the first-named conduit means between the utilization device and the condensate collecting chamber, and a second steam utilization device connected to said chamber.

3. In a steam utilization system, a boiler, a first steam utilization device, a condensate collecting chamber, conduit means connecting said boiler, utilization device, and chamber to define a closed system, a vent valve connected to said chamber, additional conduit means connecting the high pressure side of the boiler to'said chamber, a second valve in said additional conduit means, a pressure-responsive device connected between said chamber and the high pressure side of the boiler and arranged to selectively control said valves in accordance with variations of the difference in pressure between said chamber and the high pressure side of the boiler and being further arranged to maintain a substantially constant diiference in pressure, a restriction in the first-named conduit means between the utilization device and the condensate collecting chamber, a second steam utilization device connected to said chamber, further conduit means connecting the high pressure side of the boiler to said chamber, a third valve in said further conduit means, and an additional pressure-responsive device connected between said chamber and the high pressure side of the boiler and arranged to operate said third valve only when a difference in pressure, substantially greater than said first-named difference, between the condensate collecting chamber and the high pressure side of the boiler occurs.

4. In a steam utilization system, a boiler, a first steam utilization device, a condensate collecting chamber, conduit means connecting said boiler, utilization device and chamber to define a closed system, a vent valve connected to said chamber, additional conduit means connecting the high pressure side of the boiler to said chamber, a second valve in said additional conduit means, a pressure-responsive device connected between said chamber and the high pressure side of the boiler and arranged to selectively control said valves in accordance with the variations of the difierence in pressure between said chamber and the high pressure side of the boiler and being further arranged to maintain a substantially constant difference in pressure, a second steam utilization device connected to said chamber, further conduit means connecting the high pressure side of the boiler to said chamber, a third valve in said further conduit means, an additional pressure-responsive device connected between said chamber and the high pressure side of the boiler and arranged to operate said third valve only when a difference in pressure, substantially greater than said first-named difierence, between the condensate collecting chamber and the high pressure side of the boiler occurs, and a restriction in the first-named conduit means between the first-named utilization device and the condensate chamber to maintain a substantial difference in pressure across said first-named utilization device when steam is supplied from said chamber to said second-named utilization device.

5. In a steam utilization system, a boiler, a first steam utilization device, a condensate collecting chamber, conduit means connecting said boiler, utilization device and chamber to define a closed system, a, vent valve connected to said chamber, additional conduit means connecting the high pressure side of the boiler to said chamber, a second valve on said additional conduit means, a pressure-responsive device connected between said chamber and the high pressure side of the boiler and arranged to selectively control said valves in accordance with variations of the difference in pressure between said chamber and the high pressure side of the boiler and being further arranged to maintain a substantially constant difference in pressure, a second steam utilization device connected to said chamber, further conduit means connecting the high pressure side of the boiler to said chamber, a normally closed electromagnetic valve in said further conduit means, a pressure-responsive switch connected between said chamber and the high pressure side of the boiler and arranged to close responsive to a difference in pressure greater than said first-named difference in pressure, an energizing circuit connected to said electromagnetic valve through said pressure-responsive switch, and a restriction in the first-named conduit means between the first-named utilization device and the condensate chamber to maintain a substantial ditference in pressure across said first-named utilization device when steam is supplied from said chamber to said secondnamed utilization device.

6. A steam utilization system comprising a boiler, a first steam utilization device, a condensate collecting chamber, conduit means connecting said boiler, utilization device and chamber to define a closed system, a restriction in said conduit means between the utilization device and the chamber, a normally closed electromagnetic vent valve connected to said chamber, additional conduit means connecting the high pressure side of the boiler to said chamber, a second normally closed electromagnetic valve in said additional conduit means, a first pressure-responsive switch connected between the high pressure side of the boiler and said chamber, respective circuit means connecting said switch to said valves, said switch and circuit means being arranged to energize the vent valve when the pressure diiferential across said switch is below a predetermined value and to energize said second valve when said pressure differential is above said predetermined value, the pressure in the chamber being substantially above atmospheric pressure, a second steam utilization device connected to said chamber, further conduit means connecting the high pressure side of the boiler to said chamber, a second pressure-responsive switch connected between the high pressure side of the boiler and said chamber, a further normally closed electromagnetic valve in said further conduit means, and energizing circuit means connected to said last-named valves through said second pressure-responsive switch and arranged to energize said last-named valve when pressure differential between the high pressure side of the boiler and said chamber is above a second predetermined value greater than the first-named predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS 1,999,040 Dunham Apr. 23, 1935 2,065,704 Jennings Dec. 29, 1936 2,626,756 Arbogast Jan. 27, 1953 

